1. Field of the Invention
This invention relates to measuring devices utilizing a variable color display.
2. Description of the Prior Art
Commercially available measuring instruments with monochromatic digital readout are capable of performing measurements and displaying results at a relatively fast rate. However, to determine a significance of each measured value, an operator must rapidly read displayed values and perform mental comparisons with predetermined limits. The task is much more complicated when the limits are variable.
A system for measuring radioactivity described in U.S. Pat. No. 2,643,344, issued on Jun. 23, 1953 to Ian H. McLaren et al., includes an indicator with three scales and three associated light bulbs of respectively different colors. Each of the light bulbs illuminates the indicator face with a distinctive color to indicate which measurement scale is applicable.
A digital meter described in U.S. Pat. No. 2,889,518, issued on Jun. 2, 1959 to Harold R. Hudson et al., includes a rotation counter mechanically driven by a motor which also rotates a potentiometer. The motor continues to rotate until the voltage at the wiper of the potentiometer is equal to the unknown voltage. The numerical count on the counter is then a direct measure of the unknown voltage. To indicate measurement range, lamps are placed between the different rotatable sections of the mechanical counter to indicate by lighting the decimal point for the counter reading.
A driving circuit for light emitting diodes, described in U.S. Pat. No. 3,740,570 issued on Jun. 19, 1973 to George R. Kaelin et al., utilizes special light emitting diodes that emit light of different colors in response to different currents.